JPS6222470B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a highly reliable semiconductor strain transducer whose electrical characteristics do not deteriorate even when subjected to repeated strain.

For example, as shown in FIG. 1, the semiconductor strain transducer is made by bonding a silicon element made of a concave n-type silicon substrate 1 having a thick part 12 at the periphery and a thin part 13 at the center to a fixed base 11. The structure is such that when pressure is applied, the thin wall portion 13 bends and operates as a diaphragm, and one side of the thin wall portion 13 of the n-type silicon substrate 1 is provided with a p-type gauge resistance region (hereinafter referred to as a p-type gauge resistance region) in which impurities (poron) are diffused. A p-type gauge resistor 2 (referred to as a gauge resistor) 2 is formed by a diffusion process, and the strain in the thin part 13 caused by the pressure p is absorbed by the p-type gauge resistor 2.
It is configured to detect as a change in resistance.

To form this p-type gauge resistor in a part of the n-type silicon substrate 1, a selective diffusion process using a silicon dioxide (SiO ₂ ) layer as a mask, called the planar method, is normally used. The resulting silicon device has a structure as shown in FIG.

In the figure, 3 is a lower SiO ₂ layer, 4 is a phosphor glass layer, 5 is an upper SiO ₂ layer, and 6 is an aluminum electrode.

Here, the lower SiO ₂ layer 3 film was used as a mask during selective diffusion, and the phosphor glass layer 4 provided on this lower SiO ₂ layer 3
The amount of positive fixed charge (generally referred to as N _FB /cm ² ) due to sodium ions, etc. in the SiO ₂ layer 3 is reduced, and the insulation by the pn junction between the p-type gauge resistor 2 and the n-type silicon substrate 1 is improved. The upper SiO ₂ layer 5 on the phosphorus glass layer 4 is formed by a vapor phase reaction method (CVD method), and is formed to protect the phosphorus glass layer 4, which has poor moisture resistance, from the outside. be.

A silicon element having such a configuration has the disadvantage that when used as a strain transducer, the aluminum electrodes break due to repeated strain application, making it impossible to measure electrical characteristics.

FIG. 3 shows a cross-sectional view of the vicinity of the contact portion of this type of silicon element. When forming the contact window by photo-etching, the multilayer structure film consisting of the lower SiO ₂ layer 3, the phosphor glass layer 4, and the upper SiO ₂ layer 5 is
Since the phosphor glass layer 4, which is an intermediate layer, is more easily etched than the upper and lower SiO ₂ layers 3 and 5, the phosphor glass layer is side-etched and gouged.

When an aluminum electrode is formed on this by vapor deposition, a cavity 7 is formed between the aluminum electrode 6 and the multilayer insulating film, and a crack 8 is generated in a part of the aluminum electrode starting from this cavity. If a silicon strain transducer in such a state is repeatedly strained, the aluminum electrodes will completely split, resulting in a disconnection accident.

An object of the present invention is to provide a method for manufacturing a semiconductor strain transducer that uses a multilayered insulating film with an excellent surface stabilizing effect and that does not cause disconnection of metal electrodes such as aluminum.

Therefore, in the present invention, a strain sensitive region is integrally formed on one main surface of a semiconductor substrate, and three layers of a lower insulating layer, a phosphor glass layer, and an upper insulating layer are formed on the main surface of the semiconductor substrate and the strain sensitive region. In the semiconductor strain transducer, an insulating layer is formed, two through holes are provided in the insulating layer on the strain sensitive region, and metal electrodes are provided in the through holes. through-holes are formed in the upper insulating layer and the upper insulating layer by different etching processes, and the through-holes formed in the upper insulating layer are larger than the through-holes formed in the lower insulating layer. be.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 4 is a sectional view of the vicinity of a contact portion of an embodiment of the silicon strain transducer according to the present invention. 1
is an n-type silicon substrate, 2 is a p-type gauge resistor, 3 is a lower SiO ₂ layer, 4 is a phosphorus glass layer, 5 is an upper SiO _{2 layer}
Layer 6 represents an aluminum electrode.

It has a two-tiered structure in which the contact insulating film window is large at the top and small at the bottom, and there is no cavity between the aluminum electrode and the insulating film. Therefore, in the silicon strain transducer of the present invention, cracks in the aluminum electrode starting from the cavity do not occur even in the vicinity of the contact portion, and breakage of the aluminum electrode does not occur even when strain is repeatedly applied.

The contact insulating film window of this structure is formed by the following method.

A lower SiO ₂ layer 3 and a phosphor glass layer 4 are applied to the surface of an n-type silicon substrate 1 having a gauge resistor 2 . Thereafter, holes with a diameter of 60 μm are made in the phosphor glass layer 4 and the lower SiO ₂ layer 3 by photo-etching. Next, an upper SiO ₂ layer 5 is formed by a gas phase reaction method,
Bake at 1000℃. At this time, the insulating film above the 60 μmφ hole has only the upper SiO ₂ layer 5, and the other parts of the insulating film have a three-layer structure of the lower SiO ₂ layer 3, the phosphor glass layer 4, and the upper SiO ₂ layer 5. It's summery.
Also, at this time, the side surface of the phosphorus glass layer is covered with the upper SiO ₂ layer 5.
covered by and not exposed.

Next, 50 μm inside the upper SiO ₂ layer 5 with a diameter of 60 μm
A window of μmφ is formed by photo-etching, but since the phosphor glass layer is not exposed to the surface and is not immersed in the etchant, a contact window without side etching can be formed.

If the contact window is formed by the two-step photo-etching method in this manner, no cavities will be generated even after the aluminum electrode is formed.

FIG. 5 shows a sectional view of the vicinity of the contact portion of another embodiment of the present invention.

Compared to Fig. 4, the difference is that the side surface of the phosphor glass layer 4 is exposed, but the contact window is larger on the outside and smaller on the inside, and it is common that there is no cavity between it and the aluminum electrode. be.

For the contact window of this structure, after forming a three-layer insulating film, first a large hole is formed only in the upper SiO ₂ layer 5 by photo-etching, and then a small hole is formed in the phosphor glass layer 4 and the lower SiO ₂ layer 3 by photo-etching. form a hole. Compared to the example shown in Figure 4, this method does not include the step of directly applying resist to the phosphorus glass layer.
It is characterized by no contamination of the phosphorus glass layer.

As described above, according to the present invention, there is no gouging of the phosphor glass layer at the contact window portion even in a multilayer insulating film having a multilayer structure, particularly a multilayer insulating film having a phosphor glass layer with a high etching rate in the middle portion.

For this reason, no cavities are generated even when electrodes are formed.
It is possible to obtain a semiconductor strain transducer in which electrode disconnection does not occur even when repeated strain is applied.

Further, in the present invention, it is preferable that the difference between the upper and lower portions of the contact window is at least twice the thickness of the insulating film. With this structure, the average slope of the contact window is less than 45 degrees, and the step coverage of the metal electrode is improved.
This results in a structure in which disconnection of the metal electrode is less likely to occur.

In this example, phosphorus glass is used as the intermediate layer.
Although the three-layer structure film of SiO ₂ -phosphorus glass-SiO ₂ has been described, the present invention can be applied to any type of insulating film when an insulating film with a slower etch rate is formed on an insulating film such as phosphorous glass. is obvious.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional view of a conventional semiconductor strain transducer, Fig. 2 is a schematic cross-sectional view of a conventional semiconductor element, Fig. 3 is a cross-sectional view of a conventional semiconductor element near a contact, Figs. The figure is a sectional view of a semiconductor element for a semiconductor strain transducer according to the present invention near a contact. 1...Silicon substrate, 2...Gauge resistance, 3...
...Bottom SiO ₂ layer, 4...Phosphorous glass layer, 5...Upper SiO ₂ layer, 6...Aluminum electrode.

Claims (1)

[Claims] 1. A strain sensitive region is integrally formed on one main surface of the semiconductor substrate, and an insulating layer consisting of three layers, a lower insulating layer, a phosphor glass layer, and an upper insulating layer, is formed on the main surface of the semiconductor substrate and the strain sensitive region. forming and providing two through holes in the insulating layer on the strain sensitive region,
In a semiconductor strain transducer in which a metal electrode is provided in the through hole, two of the lower insulating layer and the phosphor glass layer are provided.
through-holes are formed in the upper insulating layer and the upper insulating layer by different etching processes, and the through-holes formed in the upper insulating layer are larger than the through-holes formed in the lower insulating layer. A method for manufacturing a semiconductor strain transducer featuring features.